Epstein-Barr virus (EBV), a member of the herpes virus family, infects most humans and may remain in the body indefinitely, generally in the form of a latent infection. EBV can transform B- lymphocytes and cause their immortalization. EBV is said to be the cause of a number of diseases including malignancies in the immunocompromised patients. T-lymphocytes are of primary importance in controlling the transformed B-cell population. Some of the latent viral proteins are known to be important in the recognition of infected B- lymphocytes by killer T-lymphocytes. This project is designed to study T-cell cytolytic clones, that recognize portions of the Latent Membrane Protein-1 (LMP-1), which are presented to the T-cell receptor by Class I major histocompatibility complex molecules (MHC). Approximately 100 cytolytic T-cell clones have already been generated against EBV- infected B-cells and partially characterized.